Due to concerns with limited resources of petroleum-based fuels, the demand for using renewable feedstock, such as vegetable oils and animal fats, to produce hydrocarbon fuels has increased. There are a number of well known methods for making diesel fuels or diesel fuel additives from renewable feedstock. Such methods, however, have limitations including producing fuels that are not always acceptable for commercial use.
Additives for diesel fuels whereby the additives have high cetane numbers and serve as fuel ignition improvers are known to have been made. One method for making such additives includes subjecting a biomass feedstock, such as tall oil, wood oil, animal fats, or blends of tall oil with plant or vegetable oil, to a hydroprocessing method to produce a product mixture. The product mixture is then separated and fractionated to obtain a hydrocarbon product that has a diesel fuel boiling range commensurate with known diesel duel products. This method results in an additive product that is characterized as performing poorly at low temperatures. In particular, the additive has a high cloud point at 25° C.
Another method of making a hydrocarbon suitable for use as diesel fuel includes subjecting a renewable feedstock, comprising C8-C24 fatty acids, derivatives of C8-C24 fatty acids, or combinations thereof, to a decarboxylation/decarbonylation reaction followed by an isomerization reaction. The product of the isomerization reaction is a hydrocarbon suitable for use as a diesel fuel additive. This process also produces a product having a high cetane value but poor low temperature properties, such as a high cloud point at around 25° C. As such, both mentioned resultant products are useful as diesel fuel additives but not usable as diesel or jet fuel replacements. Note that jet fuel requires significantly better low temperature properties than diesel. The cloud point is the temperature at which a fuel becomes hazy or cloudy because of the appearance of crystals within the liquid fuel.
A separate process produces a middle distillate fuel useful as diesel fuel having a cloud point of −12° C. from vegetable oil. The process includes hydrogentating the fatty acids or triglycerides of the vegetable oil to produce n-paraffins and then isomerizing the n-paraffins to obtain branched-chain paraffins. This process still suffers from a cloud point at a temperature that is comparatively too high.
To date, there appear to be no processes that produce a fuel having lower cold flow requirements, i.e. a cloud point lower than −12° C. In particular, there are no known processes to produce a stand alone Jet fuel from a renewable feedstock. To this end, it is to such a process and jet fuel composition that the present invention is directed.